The present invention relates to three families of organic chemical compounds for monitoring movements of water solutions such as monitoring subterranean movements of fluids in petroleum and hydrothermal reservoirs. The term subterranean is meant to cover all aqueous-based fluids such as formation water, production water or liquids injected into oil and gas reservoirs as well as ground water and geothermal brines. In addition, the invention includes the application of the three families of chemicals in any industrial process where movement of water or aqueous solutions is monitored, for instance in tracer studies for monitoring the movement of 1,2-ethanediol used for drying natural gas in gas pipes from oil and gas wells.
The invention also concerns the use of two groups of chemical compounds for measuring and/or monitoring movements in sub-aqueous currents or streams e.g. in connection with well-to-well investigations of petrol and oil well reservoirs or geothermic reservoirs. The notion sub-water or sub-aqueous streams or currents covers all water-based fluids such as formation water, production is water injected into petrol or oil reservoirs, ground water and geothermic brines. Additionally the invention comprises the use of these two groups of chemical substances in any industrial process where it is an object to monitor, follow or map the movements of liquid streams or currents such as in trace element monitoring for measuring the movement of 1,2-ethanediol or other chemical substances used for drying natural gas from petrol or oil reservoirs.
Institute for Energy Technology (IFE) has since the nineteen sixties worked with the development of trace substances for industrial purposes. Since the beginning of the nineteen eighties the business has focused on the oil and gas industry. The main object of inter-well (well-to-well) trace element investigations is to map or monitor the stream flux or regions in the reservoir and to measure qualitatively and quantitatively the flux or stream connections between the injection and production wells. The data from the trace element monitoring in combination with ordinary production data, pressure measurements and information from well logging provide the best available basis for evaluating the pattern for the dynamic fluid streams and thereby the optimal extraction and processing of the reservoir. Due to environmental considerations radioactive trace substances have been replaced with chemical, mainly organic, trace substances, e.g. fluorinated benzoic acids in trace substance investigations performed by IFE. The environmental authorities in Norway have indicated that the use of fluorinated benzoic acids gradually should be phased out and become replaced with more environmentally friendly trace substances. There is also a continuous demand for new trace substances to be used in petrol and oil reservoirs and in geothermal reservoirs as the present tracers are gradually being used in many wells.
Rose et al. found that naphthalene sulphonates (NAS) are thermally stable and may be used as water tracers in geothermic reservoirs at temperatures up to 330° C. In an American patent Hutchins et al. have disclosed the use of a number of trace substances in sub-water streams, e.g. some naphthalene sulphonic acids. These substances may be measured in very low concentrations (micrograms per cubic meters or ppt-levels) through the use of high pressure liquid chromatography with fluorescence detection (HPLC-FLD). These analytical techniques are relatively simple compared to methods that are used for trace analyses today (GC-MS, LC-MS, and ICP-MS). The NAS tracers have been tested at IFE for their suitability as water tracers in gas and oil reservoirs with good results. Through the aid of standardized environmental tests it has not been possible to detect that naphthalene sulphonic acids as trace substances have any negative effect on the environment. A problem with the use of naphthalene suphionic acids as trace substances has been that the wells may be polluted with the same substances. This is because the concrete that often is used in the wells contains an additive that is a polymerization product between 2-naphthalene sulphonate and formaldehyde. The additive will also contain a number of different isomeric compounds of naphthalene sulphonic acids that slowly leak from the concrete and into the production water. Additives of concrete containing polymeric 2-naphthalenesulphonate type compounds have been widely used in many oil and gas wells around the world, and this may contribute to a background level also of other isomers of NAS (Crescenzi et al.).
Tests performed at IFE have shown that 4,4′-biphenyl disulphonic acid has a corresponding stability as naphthalene sulphonic acid (NAS). As for naphthalene sulphonic acids there are reasons to believe that all of the isomeric compounds of biphenyl sulphonic acid have similar properties as 4,4′-biphenyl disulphonic acid with respect to thermal stability. Some compounds from the three groups have been synthesized at IFE. One of the fluorene sulphonic acids that were synthesized and identified was 2,4,7-fluorene trisulphonic acid. The level of interference from other organic compounds in produced water from some oil wells was investigated and found to be very low. This has made the detection down to a level below 10 μg/m3 (ppt) possible in production water from these wells (FIGS. 9 and 10).
Representatives from all the three families of chemical compounds have the same high level of thermal stability as the NAS, though the thermal stability of fluorenesulphonic acids is somewhat lower than for the other two groups. Studies performed at IFE showed that the thermal stability of 4,4′-BDS was as good as for the NAS and that adsorption to rock material was low (FIG. 11). Some naphtalenemono- and naphthalenedisulphonic acids with one of the hydrogen atoms attached to the ring system substituted with either an amino or hydroxyl group have been tested for their suitability as water tracers at IFE. These groups of tracers have generally a lower thermal stability but can often be detected more selectively and at lower concentrations in a matrix of organic components present in water from oil reservoirs than the NAS. It is likely that the same will be the case for biphenyl-, fluorenesulphonic and p-terphenylsulphonic acids with one of the hydrogen atoms substituted by an amino or hydroxyl group.
4,4′-biphenyl sulphonic acid may be detected down to a level of 100 μg/m3 (ppt) without any up-concentration in the production water from an oil field in the North Sea, and 10 μg/m3 may be detected after up-concentration.
On account of the similarities between the polyaromatic hydrocarbons concerning chemical properties and thermal stability, it is expected that the fluroene sulphonic acids also have the same degree of thermal stability and detection capability as the naphthalene sulphonic acids and 4,4′-biphenyl disulphonic acid. Some naphthalene mono and naphthalene disulphonic acids, wherein one of the hydrogen atoms in the aromatic rings has been exchanged with an amine or a hydroxy group, have been tested with respect to their properties as tracers in petrol and oil reservoirs by IFE. These substances have proven to possess a lower thermal stability than the pure naphthalene sulphonic acids, but as a compensation they may in many cases be detected more specifically with respect to the background of other organic compounds that are present in production water from petrol and oil reservoirs, and they may also be measured at even lower concentrations. Representative members from all the three groups of chemical compounds have high thermal stability such as naphthalene sulphonic acids, even if the stability of fluorene sulphonic acids appear to be somewhat lower than for the other two groups. Studies performed at IFE have proven that the thermal stability of 4,4′-biphenyl disulphonic acid was equally good as for naphthalene sulphonic acids and that the adsorption to rock material was small (FIG. 11). Some naphthalene mono- and naphthalene disulphonic acids wherein one of the hydrogen atoms in the aromatic rings have been replaced with an amine or a hydroxy group, have been tested with respect to their properties as tracers in petrol and oil reservoirs by IFE. These compounds have been proven to possess lower thermal stability than the pure naphthalene sulphonic acids, but as a compensation they may in many cases be detected more specifically with respect to the background of other organic compounds that may be present in production water from petrol reservoirs and they may be detected at even lower concentrations. Consequently it is probable that the same is valid for biphenyl, fluorene and p-terphenyl sulphonic acids with a hydrogen atom exchanged for an amine or hydroxy group.